The use of bitumen in the manufacture of materials for highway and industrial applications has been known for a long time: bitumen is the main hydrocarbon binder used in the field of road construction or civil engineering. To be able to be used as a binder in these different applications, the bitumen must have certain physico-chemical and mechanical properties. It is well known that the mechanical properties of pure bitumens can be modified by the addition of polymers.
Numerous polymers have been used in bitumen/polymer compositions, such as for example styrene and butadiene copolymers, in order to improve the rheological properties of pure bitumens. It is also well known that the physico-chemical properties of bitumen/polymer compositions are further improved when the polymers are cross-linked with sulphur for example. However, during the preparation of the bitumen/polymer compositions cross-linked with sulphur, the cross-linking is accompanied by emissions of hydrogen sulphide (H2S). Hydrogen sulphide is a colourless and toxic gas, having a characteristic odour at very low concentrations. Environmental constraints make it necessary to reduce or even eliminate emissions of hydrogen sulphide in particular during the cross-linking of polymers in the bitumen/polymer compositions.
In order to reduce the emissions of hydrogen sulphide, numerous patents describe the addition of inhibitors during the cross-linking with sulphur of bitumen/polymer compositions. In patent FR2254609, a process for reducing the emission of hydrogen sulphide by hot mixtures containing sulphur and bitumen is claimed. In order to reduce the emissions of hydrogen sulphide, a hydrogen sulphide suppressant is added to a bitumen/sulphur mixture. This suppressant is chosen from free radical inhibitors and redox catalysts. Tetramethylthiuram disulphide may be mentioned for example as a free radical inhibitor and iron chloride as a redox catalyst.
In patent EP0121377, a process is described, for preparing a mixture comprising bitumen and elemental sulphur making it possible to reduce the release of hydrogen sulphide. In this process, the agent making it possible to reduce the release of sulphide is a metal carboxylate or naphthenate. Zinc stearate is one of the preferred compounds.
In the application WO2005059016, sulphur pellets comprising a hydrogen sulphide suppressant are described. The agent is chosen from free radical inhibitors and redox catalysts. The preferred agent is iron chloride.
In application WO2005065177, a process for reducing emissions of hydrogen sulphide is described. In this process, a metal salt is added to the bitumen and to the sulphur. Zinc oxide is one of the preferred compounds.
In patent EP0907687, a process is described for cross-linking bitumen/polymer compositions where different functionalizing agents are used. These functionalizing agents are chosen from carboxylic polythiolesters and/or polythioethers, there is no indication that the functionalizing agents described make it possible to reduce emissions of hydrogen sulphide.